During the pre-war years, the Japanese Navy had painstakingly prepared its fleet for one particular strategy: a “decisive battle” to be held in its home waters, after the US fleet had been whittled down by aircraft and submarines during its long transit from Pearl Harbor into Japanese waters. The fleet was designed for this task, where fuel endurance and habitability and (in some cases) ships’ stability was sacrificed for speed and firepower. Logistics ships, tenders, repair ships, and developed forward support bases were unneeded in this strategy. Bases were to receive only minimal development, enough to support long-range reconnaissance and bombing aircraft and a sacrificial garrison. They were only speed bumps in the path of the American fleet and likely to be lost to the Americans’ advance. Fleet auxiliaries were not needed, because the most intense combat was expected to occur near the Japanese homeland in one cataclysmic decisive battle.
When the Japanese government decided on a war of conquest, this strategy was set on its ear. Now, the Navy would be required to take and hold outlying islands as a way to prevent the Allies from retaking the vital natural resources areas the Japanese would conquer in order to sustain their warfighting machine. The decisive battle was moved further and further from Empire waters until it eventually was in the vicinity of the Marshall Islands, 2,300nm from Japan. Now bases would be needed and auxiliaries commissioned to service the fleet far from its homeports, but the very lack of resources that would force Japan into the war would also prevent her from establishing the needed bases and auxiliaries.
But first, the Japanese had to achieve the desired conquests, a process which, even in the force vacuum in the Pacific caused by the war in Europe, was likely to take months. The Japanese would need most of their fleet for the offensive, scattered over thousands of miles supporting multiple simultaneous thrusts. The wild card was the United States Pacific Fleet. While it consisted of less than half the Americans’ commissioned battleships, it could be reinforced, and a move by the fleet to the Philippines would cut off the Japanese lines of communication to the southern advance, cut off resources returning to Japan, and threaten the Japanese with defeat.
Yamamoto proposed a strike against the Pacific Fleet’s main base at Pearl Harbor, using all his available fleet carrier strength. What is clear is that Yamamoto was after battleships, mainly to strike a psychological blow against the United States, hoping that it would result in a negotiated peace after the Japanese had secured their conquests. In the shadow of the historical results of the Pearl Harbor attack, what is little understood is that Yamamoto (and the rest of the Japanese command structure) was expecting to sacrifice at least two fleet carriers to this goal and perhaps more, making it a “carriers for battleships” swap. This realization belies the previous general assumption that Yamamoto was an aviation visionary who believed battleships to be obsolete. This is confirmed by Yamamoto’s instructions to Kido Butai, ordering them to press their attack even if they were detected 24 hours before the strike, and to attack even if there were no carriers in Pearl Harbor. Clearly, Yamamoto was willing to put his fragile carriers in harm’s way in order to cripple battleships.
Japanese testimony indicates that they needed to cripple four American battleships. This number was likely based on the calculations used to determine the needed force ratios to defeat the American fleet after a trans-Pacific advance. This number is confirmed by back-calculating from the targeted ratios that the Japanese attempted to obtain in negotiations during the various naval arms limitations conferences between 1922 and 1936. Even then, there would be little margin for a Japanese victory—they admitted that, if the confrontation occurred as planned, they had only a 50-50 chance of victory, a rather low chance of success considering that the fate of the country was at risk.
Yamamoto’s avowed objective was to cripple the Pacific Fleet sufficiently to prevent it from moving against the flank of the Japanese advance for at least six months. What is not commonly recognized is that this objective put the torch to the conventional Japanese plans for a decisive battle between the fleets at odds that would allow a Japanese victory. In fact, if the Americans were delayed by six months, they would have no incentive to engage the Japanese in a fleet action until their strength was sufficiently reinforced by the oncoming flood of new construction. A successful attack against Pearl Harbor would force the Americans into a “long war” strategy from the outset, exactly the kind of war that the Japanese knew they could not win. Yamamoto recognized this. After the conquest of resource areas, he had to force the Americans’ hand. He needed a decisive battle by whatever means possible. He tried to force one in the middle of the Pacific, which then led to defeat at the Battle of Midway.
The most telling indictment against the Japanese strategists and intelligence service is that they did not need an attack on Pearl Harbor to get their needed six months. It would have taken six months for the Americans to assemble sufficient oilers and auxiliaries to permit significant offensive operations, assuming that the course of the war in Europe allowed such a concentration. Raids would have been possible, but nothing serious enough to influence the course and outcome of Japan’s phase-one expansion to the south. Generally blind to logistics constraints, the Japanese did not care to visualize or understand the constraints under which the Americans would operate.
Contrary to the accolades of most chroniclers, the planning and execution of the Pearl Harbor attack was imperfect; in many ways it was not state-of-the-art.
• The planning was inflexible. The battleship-killers, the B5N Kates, the only Japanese carrier attack bombers that could carry either heavy armor-piercing bombs or torpedoes, were allocated their weapons very early in the planning process. This allocation was not adjusted to account for the results of training and tests, or intelligence regarding the presence or absence of torpedo nets in Pearl Harbor. The problems associated with delivering torpedoes in shallow water were solved literally only two weeks before the expedition departed home waters.
• The planners were to execute the attack even if the torpedo delivery problem had not been solved, or if the battleships were protected by torpedo nets. This contributed to the decision to over-allocate B5N Kates to the high-altitude bombing role.
• Although the level bombers exceeded accuracy expectations, a disgraceful number of their AP bombs failed to properly explode.
• In another example of inflexibility, the Japanese received a detailed intelligence report 24 hours ahead of the attack, yet did not adjust their plan to the observed conditions. The staff planners were so intent upon sinking carriers that they decided to allow an attack against the carrier anchorage to remain in place after learning there were no carriers in port.
• Had more B5N Kates been assigned to carry torpedoes the attack would have been considerably more lethal. As it was, three of the eight viable torpedo targets were untouched, and one was hit only by mistake.
• The plan was based entirely upon achieving a surprise attack, and provided for no SEAD support for the torpedo bombers. Even when a “no surprise” plan option was included, the torpedo bombers were not provided with any support—indeed, they were not even escorted the entire way to the target by fighters.
• The plan for the torpedo bombers was faulty. Planned attack routes were not deconflicted and caused mutual interference.
• The Japanese scheme of prioritizing targets was unexecutable. The burden of responsibility was put onto the individual aircrews, who could not have the information needed to appropriately execute the plan, and did not have the needed communications to mutually coordinate their efforts. The result was an overconcentration on the easiest targets, wasted torpedoes, and the escape of half the major targets on the torpedo prioritization list. Eleven torpedoes accomplished the mission—the rest were misses, overkills, or hits on inappropriate targets.
• Fuchida’s mistake with the flares, rather than an inconsequential error, threw the torpedo bombers’ attack into some confusion and rushed their approach. This gaffe was a contributing factor to the problems the torpedo bombers faced, including mutual interference, aborted runs, and likely a reduction in delivery accuracy and reliability. Fuchida’s error directly contributed to the B5N Kate aircraft losses.
• The loss of Arizona was the result of a bomb that penetrated the ship’s forward magazine, not the convoluted explanation in the Navy’s official report. Simulation modeling shows that the hit was not a “one in a million” outlier, but the most probable result for the attack.
• Japanese aerial communications were ineffective.
• The Japanese leaders could not exert effective control over the strike, especially after Fuchida’s error with the flares turned the first wave into an aerial Preakness.
• The attack formation adopted for the torpedo bombers, long strings of up to 12 bombers separated by 500 yards or more (which often became 1,500 to 1,800 yards under combat conditions), eliminated any possibility of anything but the most basic “follow the leader” control of targeting.
• The attacks by the dive-bombers on Nevada were an inappropriate employment of the planes’ ordnance. These bombs did nothing towards accomplishing the mission of the attack.
• The idea of sinking a warship in the channel in order to bottle up the Pacific Fleet was a quixotic half-measure, an exceedingly poor decision.
• The dive-bombers assigned to fleet targets contributed little. Of 81 bombers tasked with this mission only two hits were accomplished against what should have been their primary target, cruisers. Six of the eight cruisers in harbor escaped significant damage, with the other two were damaged by torpedo hits. Much of the damage caused by the dive-bombers came from bombs that missed their intended targets.
• A disgraceful percentage of the dive-bombers’ 250kg bombs were defective.
• The dive-bombers’ target identification was exceedingly poor. Tenders were identified as battleships and cruisers, destroyers identified as cruisers, drydocks identified as battleships.
• The plan for the employment of the fighters was poor. Fighter cover for the first wave’s bombers was not in accordance with the importance of the attack groups. Unbelievably, the torpedo bombers were not escorted all the way to the target, and had no top cover for the duration of their attack.
• Much of the “conventional wisdom” about the attack is false:
• The Japanese did not employ a corps of “super aviators” for the attack.
• Any third wave attack directed against the shipyard could have damaged only a small part of Pearl Harbor’s total repair capacity. Any damage could have been put to rights rapidly, and would not have caused the war in the Pacific to be extended by any appreciable period.
• While the fuel tanks were vulnerable and the majority of them could have been destroyed in a third wave attack, the effects of their destruction could have been mitigated. Damage to the fuel tanks would not have put back the course of the war by any significant duration and would not have forced the Pacific Fleet to abandon Pearl Harbor as some have asserted.
• The Japanese fourteen-part diplomatic message, delivered late and after the attack, was not a declaration of war. An on-time delivery would not have changed the American people’s righteous anger catalyzed by the Japanese “sneak attack.”
• The probability that the fifth midget submarine penetrated into the waters adjacent to Battleship Row and torpedoed Oklahoma or Arizona is vanishingly small.
One significant discovery is the extent to which many historians have been wrong in their opinions of the battle. This has in turn led to much distortion in the historical assessments of the roles, skills, and judgment of the participants. Care must be taken before previous historians’ value judgments are accepted. Even the most prestigious of the contemporary warfighters might be wrong.